The present invention relates to a roller bearing apparatus, a method of producing the roller bearing apparatus, and a cover attached to the roller bearing apparatus.
Some roller bearing apparatuses that support wheels, for example, of vehicles are provided with a rotation number detector that detects the rotating speed of the wheel for controlling the anti-lock brake system and the like. Such roller bearing apparatuses are provided for example, as shown in FIG. 11, with a roller bearing comprising an inner ring 51 as a rotary ring that co-rotates with a flange 50 to which a wheel is attached and an outer ring 52 that interposes multiple rolling elements between itself and the inner ring 51 and is attached to a vehicle body, and a closed-end cylindrical cover 54 attached to the outer ring 52 and carrying a rotation number detector 53 that detects the rotation number of a wheel. An end 54a of the cover 54 is fitted in the outer ring 52 against its inner periphery so as to close the opening of the outer ring 52 at one end.
If muddy water or foreign substances enter the interior of the roller bearing apparatus described above, the roller bearing apparatus deteriorates in terms of durability or detection accuracy of the rotation number detector 53. Therefore, the end 54a of the cover 54 is pressed in the outer ring 52 against its inner periphery for increased sealing.
The cover is conventionally produced by pressing a metal plate. However, synthetic resin covers produced by injection molding using a metal mold have been recently proposed in place of metal covers in order to reduce the cost (for example, see Japanese Unexamined Patent Publication No. 2001-318105).
However, using a synthetic resin cover has the following problems.
The synthetic resin cover 54 and metal outer ring 52 have different thermal expansion coefficients. When the temperature of the roller bearing apparatus rises, a small clearance may occur between the outer ring 52 and the cover 54, deteriorating the seal.
When there is clearance between the inner periphery 52a of the outer ring 52 and the outer periphery 54a1 of the opening end 54a, there has been proposed to form a groove 54b at the outer periphery 54a1 for creating a labyrinth effect together with the clearance, thereby preventing muddy water from entering the interior of the roller bearing (for example, see Japanese Unexamined Patent Publication No. 2004-76753).
However, the roller bearing apparatus described in Japanese Unexamined Patent Publication No. 2004-76753 still allows a small clearance between the inner periphery 52a and the outer periphery 54a1, making it desirable to improve the sealing between the inner periphery 52a and the outer periphery 54a1 in order to ensure durability.
In some prior art bearing apparatuses, the cover is provided with a sensor mount having a seating face as a sensor-mounting reference level. Abutting the seating face, a sensor is mounted on the sensor mount, by which the sensor and an encoder that is attached to and co-rotates with the rotary ring are provided at a specific distance. However, in the synthetic resin cover, some forms of the sensor mount may sink (deform) as a result of thermal contraction of the synthetic resin in the course of molding, and the seating face of the sensor mount of the prior art cover will not be accurately formed, requiring post processing in order to use the seating face as a sensor-mounting reference level. Specifically, a tilted seating face resulting from such deformation must be, for example, flattened to a level seating face by means of cutting and the like.
Known structures for mounting a sensor include a sensor insertion opening formed in the cover through which a sensor body is inserted. In such case, the sensor is provided with a flange and a cap nut is embedded in the cover, and the flange is fixed to the cover with a bolt with the use of the cap nut (for example, see Japanese Unexamined Patent Publication No. 2003-13982). The end face of the cap nut and the cover surface are in one plane (so-called leveled), to which the sensor flange is abutted and bolted.
In the mounting structure described in Japanese Unexamined Patent Publication No. 2003-13982, the sensor is fixed by a bolt at the flange, so that secure fixation of the sensor is performed as compared to a sensor having no flange. When the cover is made of synthetic resin, the cap nut is easily placed in the cover by insert resin molding, which allows the cover to be produced at reduced cost. Further, the cap nut to be embedded in the cover is easily immobilized therein. The sensor flange is abutted to the cover surface, so that the sensor is axially positioned with increased accuracy as compared to a sensor having no flange.
However, being made of a synthetic resin, the cover easily sinks or warps in the course of molding. Therefore, when the flange is abutted to the cover, the sensor may be tilted or axially dislocated by the warpage of the cover, problematically deteriorating the sensor gap accuracy.